The Phase Stability of V.L.F. Signals on Polar Paths

Measurements of the phase and field strength of the received signal from the very low frequency (v.l.f.) radio transmitters located in the U.K. and U.S.A. have been made at various places throughout the world. Considerable effort has been extended in analysing the resulting data with the object of distinguishing between normal and abnormal propagation phenomena. The notable fact which has emerged is that there is a remarkable day to day stability exhibited by both the phase and amplitude of the received signals. For most practical purposes it if the phase of the signal which is of greatest use, and the paper is mainly concerned with this phase stability. It is shown that within certain limits, to be discussed, the diurnal phase variations are sufficiently stable for the phase to be used in a navigation system, even on polar paths.